This program is directed at the Research and Development of a high energy density, electrically rechargeable bipolar Nickel-Metal Hydride (Ni-MH) battery to serve as the internal power supply for a Ventricular Assist Device (VAD). The internal battery pack should store enough energy for 45 minutes of operation in order to give the recipient of such systems maximum portability. The battery pack should be as small and lightweight as possible and have a life of five years. Presently, rechargeable Ni-MH batteries are commercially available utilizing conventional monopolar spirally-would cylindrical cells. Implantable prismatic battery packages comprised of cylindrical cells deplete spare body cavities due to intercell voids. The proposed bipolar Ni-MH system has the potential of being less than one half the size of present technology Nickel-Cadmium (Ni-Cd) batteries, the only other presently viable battery system, by virtue of more efficient use of volume. In addition to excellent performance, the Ni-MH system offers safe operation and employs abundant and environmentally benign materials. Based on the bipolar concept demonstrations and past activities this program is directed at the development of an advanced bipolar configuration of the Ni-MH system to maximize volumetric energy density. The goal is to develop a battery that delivers greater than 70 Wh/kg, 238 Wh/1, has a life of five years (1826 cycles at one cycle per day) at 75 percent DOD and is compatible with implantable operation. PROPOSED COMMERCIAL APPLICATION: Rechargeable batteries are used in military equipment, portable electronics (cellular phones, camcorders, portable computers, medical instruments and electric vehicles). Improved Ni-MH batteries would successfully compete in all of these applications and offer increased safety and environmental characteristics over presently available battery systems.